Electrochemical sensors for testing water

ABSTRACT

An electrochemical sensor for the detection and analysis of an analyte in a solution is disclosed. The electrochemical sensor has an electrically non-conductive support; a plurality of electrodes on the support, each electrode formed from an electrode material and having a first surface and an opposite second surface, said first surface facing towards the support and the second surface facing away from the support. The plurality of electrodes includes a reference electrode, a counter electrode, and a working electrode. The working electrode has a reagent composition containing a reagent for detecting an analyte applied directly to the second surface of the working electrode or dispersed throughout the electrode material of the working electrode.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.14/033,795, filed Sep. 23, 2013, which is a CIP of U.S. patentapplication Ser. No. 14/032,891, filed Sep. 20, 2013, claims priorityunder 35 U.S.C. § 119(e) from Provisional Application No. 61/704,139filed Sep. 21, 2012, the disclosures of which are incorporated herein byreference.

FIELD OF THE INVENTION

The present invention relates to an electrochemical sensor for detectionand analysis of one or more analytes in water.

BACKGROUND OF THE INVENTION

Chemicals have been added to pools and other water supplies to disinfectand sanitize the water so that the quality of the water is useable forits intended purpose. There are a number of factors that affect waterquality, including water chemistry parameters. The major chemistryparameters that are associated with maintaining water quality includesfree available chlorine, total available chlorine, total hardness, totalalkalinity, pH, cyanuric acid, as well as copper. It is thereforeimportant to monitor and control these chemistry parameters for waterquality management, especially for water such as recreational andindustrial water.

Chlorine disinfects or sanitizes water by destroying harmfulmicroorganisms, such as bacteria, fungi, and viruses and also controlsnuisance organisms, including algae that may be occur in recreationalwater, filtration device, and piping. Available chlorine is the majorcomponent of chlorine species, which is mainly composed of a class ofchemicals that produce hypochlorous acid (HOCl), when is dissolved inwater. When chlorine, either as gaseous chorine, sodium hypochlorite, orcalcium hypochlorite dissolves in water it produces HOCl, and at the pHrange of 5-6 chlorine exists as HOCl:

Cl₂+H₂O ═HOCl+H++Cl⁻

NaOCl+H₂O═HOCl+Na⁺+OH⁻

Ca(OCl)₂+2H₂O═Ca(OH)₂+2HOCl

The hypochlorous acid may then dissociate into hydrogen ions (H⁺) andhypochlorite ions (OCl⁻) and the hypochlorite ions (OCl⁻) become morepredominant at higher pH of 7.2-7.5.

HOCl=H⁺+OCl⁻

Chlorine in the forms of Cl₂, HOCl, or OCl⁻ is known as free availablechlorine, and these three forms of chlorine may present in water andtheir relative amounts in water depends on pH and to a slight extent ontemperature.

Combined available chlorine refers to any chlorine species associatedwith inorganic chloramines (NH₂Cl and NHCl₂) and organic chloramines(RNHCl, R=alkyl) in water. Total available chlorine is the sum of freeavailable chlorine and combined available chlorine. The relative amountof combined available chlorine also depends on pH and temperature, andthe concentration of inorganic or organic amines in water. However, thecombined chlorine undergoes limited hydrolysis in water and has lessoxidizing power than free available chlorine. It is therefore importantto distinguish free available chlorine and combined available chlorineto measure the disinfection strength of residual chlorine.

Total hardness is the measure of water hardness. Calcium and Magnesiumions are the primary sources of water hardness. In general, calciumrepresents about 97% of the water hardness in pool water and the levelof dissolved calcium is kept ideally between 200 to 500 ppm. Pool waterrequires the appropriate level of water hardness. High calcium hardnesscan result in cloudy water and scale formation due to the precipitationof calcium carbonate from the water, whereas low calcium can lead tocorrosion.

Total alkalinity is the measure of the pool water's buffering capacityto resist pH change. The buffering capacity of alkalinity in water isdue to carbonate, bicarbonate, hydroxide, and sometimes borates,silicates and phosphate, but is mainly measured by the amount ofcarbonate and bicarbonate in pool water. Further, at a desirable pHrange of 7.2-7.6 in pool water most of the carbonate ions are in thebicarbonate ions from which buffering is provided. In general, totalalkalinity is kept between 60-150 ppm depending on the sanitizing systembeing used and without a proper control of total alkalinity pH of thewater rises or falls abruptly, causing the water to form scale andbecomes cloudy or corrosive. The level of total alkalinity is tested andadjusted before adjusting pH.

Cyanuric acid content in pool water is important because cyanuric acidis functioning as free available chlorine stabilizer in water byprotecting the free available chlorine against UV light degradation.Thus, maintaining sufficient cyanuric acid levels in water is importantfor maintaining sufficient levels of free available chlorine.

There are a number of sources for copper to enter the pool waterincluding different water sources and algaecide, and dissolved coppercan lead many pool water issues and public concerns. For example, highlevel of copper can result in ugly staining. Thus, keeping the level ofdissolved copper in the pool water as low as possible is important formaintaining water quality.

There is a continuous interest in developing simple, rapid, and reliablemethods for the determination of water chemistry parameters including,but not limited to, free chlorine, total chlorine, total hardness, totalalkalinity, pH, cyanuric acid and copper. For example, because chlorinespecies in water are very reactive and may dissipate very quickly thereliable and accurate measurements of residual chlorine in water aredifficult. There are a number of field test kits available for thedetermination of free and combined available chlorine in water, which ismostly based on the use of DPD (diethyl p-phenylenediamine). DPD testkits are manufactured with either liquid, powder or tablet reagents.Test kits that are currently available for the analysis of waterhardness and total alkalinity are based on the use of specific dyereagents or acid-base indicators, followed by the spectrometric analysisor titration where changes in color in test solution are monitored.However, there are often interferences and human error in monitoring thecolor change for testing for hardness or alkalinity in water, leading toerroneous test results. At present, there are no simple, rapid, costeffective and reliable diagnostic test kits or devices to accurately andeasily measure the contents of free chlorine, total chlorine, totalhardness, and total alkalinity in recreational water. The presentinvention provides an answer to that need.

SUMMARY OF THE INVENTION

In one aspect, the present invention provides an electrochemical sensorfor detection and analysis of an analyte in a solution. Theelectrochemical sensor has an electrically non-conductive support; aplurality of electrodes on the support, each electrode formed from anelectrode material and having a first surface and an opposite secondsurface, said first surface facing towards the support and the secondsurface facing away from the support. The plurality of electrodesincludes a reference electrode, a counter electrode, and a workingelectrode. The working electrode has a reagent composition containing areagent for detecting an analyte applied directly to the second surfaceof the working electrode or dispersed throughout the electrode materialof the working electrode.

The electrochemical sensor of the present invention may have workingelectrodes for the detection and analysis of water for free chlorine,total available chlorine, total alkalinity, total hardness of the water,pH, cyanuric acid and copper.

In another embodiment of the present invention is directed to method ofanalyzing water. The method includes placing the electrochemical sensorin a display device and placing the electrodes of the sensor in water tobe analyzed.

These and other aspects will become apparent when reading the detaileddescription of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a top plan view of the electrochemical sensor having asingle working electrode.

FIG. 2 shows an exaggerated cross-sectional side view of theelectrochemical sensor along section line 2-2 viewing the workingelectrode with the reagent composition deposited on the electrode.

FIG. 2A shows an exaggerated cross-sectional side view of theelectrochemical sensor along section line 2-2 viewing the workingelectrode with the reagent composition dispersed throughout theelectrode material instead of deposited on the electrode as shown inFIG. 2.

FIG. 3 shows an exaggerated cross-sectional side view of theelectrochemical sensor along section line 3-3 viewing the counterelectrode.

FIG. 4 shows an exaggerated cross-sectional front view of theelectrochemical sensor along section line 4-4 viewing the electrodeswith the reagent composition deposited on the electrode.

FIG. 5 shows a top plan view of the electrochemical sensor having aplurality of electrodes.

FIG. 6 shows a plot graph of calcium hardness detected over time withthe electrochemical sensor of the invention.

FIG. 7 shows a plot graph of cyanuric acid (CYA) over time detected withthe electrochemical sensor of the invention.

FIG. 8 shows a plot graph of dissolved copper detected over anincreasing electric potential with the electrochemical sensor of theinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

To gain a better understanding of the present invention, attention isdirected to the drawings. The drawings are not intended to be limitingbut are intended for understating the present invention. It has now beensurprisingly found the electrochemical sensor of the present inventionis able to perform without the need of (i.e., omits) an intermediatelayer between the electrode and the reagent composition. It has beenfound that the sensor of the present invention has simplicity ofmanufacture and has sensitivity to give a sensor with reproducibleresults.

Turning to FIG. 1, shown is a top view of the electrochemical sensor 10.The electrochemical sensor 10 has a support 12 which has a plurality ofelectrodes 14 disposed on support 12 and formed from an electrodematerial. The electrodes 14 may be disposed on both sides of the supportor only on one side of the support. The electrodes 14 are spaced about asuitable distance so that the electrodes 14 are independent from eachother. Electrodes 14 include a reference electrode 16, a counterelectrode 18 and a working electrode 20. Operation of each of theseelectrodes will be described in more detail below. As can be seen inFIGS. 2 and 3, each electrode 14 has a first surface 21 adjacent support12 and a second surface 22, which is opposite the first surface 21 andthe second surface 22 faces away from the support 12. As can be alsoseen in FIG. 2, electrode 14 includes working electrode 20 with reagentcomposition 26 directly deposited on (i.e., applied to) second surface22. In another embodiment, as seen in FIG. 2A, electrode 14A includesworking electrode 20A with first surface 21A and opposite second surface22A. As can be seen further in FIG. 2A, working electrode 20A hasreagent composition 26A dispersed throughout the electrode materialinstead of being directly deposited on second surface 22A.

The support 12 also has plurality of connectors 30 disposed thereon,which serve to connect the electrochemical sensor to an instrument,which will allow a user of the electrochemical sensor 10 to takereadings from the sensor. The connectors 30 are generally on the samesurface of the support 12 as electrodes 14, but are generally positionedaway from the end of the support containing electrodes 14. It ispossible for the connectors 30 to be on the opposite end of the supportfrom the electrodes 14, as is shown in FIG. 1, or, in the alternative,connectors 30 may be located along the sides of the support 12.

The electrodes 14 are each separately electrically connected to separateconnectors 30. Each electrode 14 may be directly connected to aconnector 30, or may be connected via a conductive track 40 which isdisposed on the support 12. Each conductive track 40 serves to connect agiven connector 30 to a given electrode 14, without crossing anotherconductive track 40. To protect the conductive tracks 40, a protectivecoating 50 is optionally applied over the support 12, in all or most ofthe area in which the conductive tracks 40 are present.

Support 12 is prepared from a material which is electricallynon-conductive and inert to the testing environment and chemicalsapplied thereto to form the electrodes 14, the connectors 30 and theconductive tracks 40. Suitable materials useable for the supportinclude, for example, ceramic, paper, plastic or glass materials.Generally, from a standpoint of cost and durability, the support 12 isgenerally flexible to a degree so that the support 12, electrodes 14,connectors 30 and conductive tracks 40 are not damaged due to handlingprior to use. Generally, support 12 is prepared from a dielectricplastic material. Exemplary plastic materials usable for the supportinclude polyester, polycarbonate and polyvinylchloride. Other polymericplastic materials may also be used without departing from the scope andspirit of the present invention. Ideally, the support should have a costassociated therewith which allows the sensor to be disposable after use.

The electrodes 14 may be disposed on the support using any of a varietyof techniques known to those skilled in the art. Suitable techniquesinclude, for example, screen printing, lithography, vapor deposition,spray coating, vacuum deposition, inkjet printing or other similartechniques. Each electrode 14 is prepared from a conductive compositionwhich is applied to the support 12. Suitable conductive compositionsinclude conductive inks with may be screen printed or inkjet printedonto the support 12. Conductive inks include inks that containconductive particles in the ink. Exemplary conductive particles includemetal particles of conductive metals, such as gold, silver, platinum andconductive noble metal, carbon particles or other similar conductivepolymers. In one embodiment of the present invention, the materials thatmay be used for the counter electrode 18 and the working electrode 20include carbon, metal or metal-carbon mixture. A silver based ink or asilver/silver chloride based ink may be used for the reference electrode14. Generally, silver/silver chloride based inks are used for thereference electrode 14.

The connectors 30 may be prepared from any conductive material includingcopper, gold, silver, platinum or other similar conductive metals.Generally, the connectors 30 will be prepared from the same ink materialused to prepare one or more of the electrodes, from an ease ofmanufacture standpoint. In one embodiment of the present invention, theconnectors 30 are each prepared from the same material used to preparethe reference electrode 14. For example, the connectors may be preparedform a silver/silver chloride based ink.

The connecting tracks 40, when present, are also prepared from aconductive ink and is applied using the same techniques mentioned abovefor the disposition of the electrodes to the substrate. Generally, theconnecting tracks 40 will be prepared from the same ink material used toprepare the connectors 30 or electrodes 14. By using the same material,the sensor can be quickly and easily manufactured. In one embodiment,the connecting tracks are prepared from a silver/silver chloride basedink.

To protect the connecting tracks 40 from damage prior or during use, andto prevent the connecting tracks 40 from acting like a referenceelectrode, if they come into contact with the water to be tested,connecting tracks 40 may be provided with a protective insulationcoating 50. Protective insulation coating 50 can be prepared from anyelectrically non-conductive material that will effective adhere to thesupport 12 and the conductive tracks 40. Exemplary materials include,for example, dielectric polymeric materials such as polyesters,polyvinyl chloride and other similar compatible polymers. It is notedthat the protective coating does not need to cover the entirety of theconnecting tracks 40, but will need to cover the connecting tracks wherethe connecting tracks 40 connect to the electrodes 14. This will preventthe connecting tracks 40 from coming into contact with the water to betested, as the electrodes 14 are placed in the water to be tested.

In the present invention, reference electrode 16 and counter electrode18 are prepared from different materials. Generally, working electrode20 is prepared from the same material as the counter electrode 18;however, working electrode 20 has a reagent composition 26 applied tothe second surface 22 of the working electrode 20, as is shown in FIG.2, which show a cross-section of the electrochemical sensor 10, alongsection line 2-2 in FIG. 1. Alternatively, the working electrode (shownas 20A in FIG. 2A) has the reagent composition (shown as 26A) mixed withelectrode material making up the working electrode to disperse reagentcomposition 26A throughout working electrode 20A. The reagentcomposition 26 applied to the working electrode 20, or mixed with theelectrode material, determines the analyte that the working electrode 22will detect and analyze. Comparing the cross-section of theelectrochemical sensor along the working electrode 20 shown of FIG. 2 tothe cross-section of electrochemical sensor along the counter electrode18 shown in FIG. 3, it can be seen that the counter electrode 18 doesnot have a reagent composition 26 applied thereto, while workingelectrode 20 does. FIG. 4 shows the front-side view of theelectrochemical sensor 10 of the present invention. Again, it can beseen that the working electrode 20 has a reagent composition 26 appliedto the second surface 22 of the working electrode 20. Alternatively, ascan be seen in FIG. 2A, the reagent composition can be dispersedthroughout the electrode material of the working electrode. It can alsobe seen that the reference electrode 16, the counter electrode 18 andthe working electrode 20 are spaced apart on the support 12. This allowseach of these electrodes to be electrically insulated from one another.

The reagent composition applied to, or dispersed within, the workingelectrode is modified with appropriate reagents for the individualdetection of free chlorine, total chlorine, calcium hardness, pH,cyanuric acid, copper, or total alkalinity. Each working electrode willhave a reagent composition applied to the second surface of that workingelectrode. The sensor 10 may have multiple working electrodes, as shownin FIG. 5. As can be seen in FIG. 5, there are multiple workingelectrodes 201, 202, 203. Each working 201, 202 and 203, may have adifferent reagent composition applied to the surface. Alternatively,when multiple working electrodes are present, two or more workingelectrodes may have the same reagent. When multiple working electrodesare present, the only limitation to the number of electrodes is thespace available the surface of the support 12. It is contemplated thatelectrodes could be on both sides of the support. Generally, there willbe between about 1 and about 8 working electrodes on the sensor.

Detection of each analyte is based on the amperometric or voltametricanalysis using a specific reagent or reagent mixtures deposited on theworking electrode, or mixed with the ink prior to screen printing theelectrode on the substrate. The amperometric method is acontrolled-potential electrochemical technique, where the currentresponse to an applied potential is measured by a potentiostat. Apotentiostat is an electronic instrument that controls the voltagedifference between a working electrode and a reference electrode. Anytype of commercially available or custom-made portable, field-deployablepotentiostat may be used. In the case of labs, non-portablepotentiostats may be used. An exemplary commercially availablepotentiostat is a Uniscan Instruments, Ltd. Model PG581 Potentiostat,having office in Buxton, United Kingdoms. It is also contemplated thatother potentiostats, or other items such as smart phones withapplications (software) could also function as a potentiostats for theelectrochemical sensors of the present invention. In general, the sensoris polarized at a potential value (vs. Ag/AgCl) for a time period. Thecurrent observed at a given time is recorded and averaged using thesoftware embedded in the potentiostat. The concentration of analyte isthen determined using the average current value and the pre-loadedcalibration table in the instrument.

The reagent compositions useable in the present invention will now bedescribed.

Free Chlorine Detection Reagent Composition

The free chlorine reagent composition for the free chorineelectrochemical sensor according to the invention, measures the contentof free chlorine in water by the amperometric analysis. The reagentcomposition for the free chlorine electrochemical sensor will generallycontain a redox indicator reagent, a buffer and a polymeric material.Typically, water is used as the solvent for the composition and thecomponents are added so that the resulting composition has the componentpresent in an amount disclosed below. These components are generallymixed and applied to the second surface of the working electrode. Thesolvent is removed by drying the composition at an elevated temperaturefor a period of time.

Suitable redox indicator reagents include, for examplep-phenylenediamine salts, N,N-diethyl-p-phenylenediamine sulfate salt(DPD), N,N-dimethyl-p-phenylenediamine sulfate salt, andN,N,N′N′-tetramethyl-p-phenylenediamine. The redox indicator reagentcomponent is added to the reagent composition to form a solution whichis about 0.01 M to about 0.20 M, and more typically in a 0.03 to about a0.07 M.

Suitable buffers include phthalate buffers, phosphate buffers. Phosphatebuffers include, for example disodium hydrogen phosphate, sodiumdi-hydrogen phosphate, and mixtures thereof. The buffer component isgenerally present in the reagent composition in the range of about 0.01to about 0.03 M.

Sodium chloride is generally added to the buffer in a concentration ofabout 0.3 to about 0.6 M. Typically, it is added in an amount of about0.4 to about 0.5 M.

In addition, the reagent composition will also have a polymericcomponent added to assist disposition of the redox indicator reagent tothe surface of the electrode. In addition, the polymeric material in thereagent composition is used to retain reagent and buffer mixture on theelectrode surface, and stabilizing the response of electrochemicaldetection. Possible polymers include, for example, polyethylene glycol,sodium alginate, polyvinyl alcohol, or other similar polyelectrolytepolymers. Generally, polyethylene glycol is used for the free chlorinesensor. Typically, the polymer is added in an amount of about 0.1 toabout 2.0% by weight, based on the volume of the solution.

In the electrochemical sensor containing a free chlorine reagentcomposition applied to the working electrode, the amount of freechlorine is measured by generating a voltage applied from the referenceelectrode and the resulting current from the working electrode ismeasured, according to the reaction shown below:

HOCl+2e−↔Cl⁻+OH⁻

The sensor is polarized at a potential value (vs Ag/AgCl) for a timeperiod. The current observed at 15-30 seconds is averaged using thesoftware embedded in the potentiostat. The concentration of freechlorine is then determined using the average current value and thepre-loaded calibration table in the instrument.

Total Chlorine Detection Reagent Composition

The total chlorine reagent composition for the total chorineelectrochemical sensor according to the invention, measures the contentof total chlorine in water by the amperometric analysis. The reagentcomposition for the total chlorine electrochemical sensor will generallycontain a potassium halide salt, a buffer component and a polymericmaterial. Typically, deionized water is used as the solvent for thecomposition and the components are added so that the resultingcomposition has the component present in an amount disclosed below.These components are generally mixed and applied to the second surfaceof the working electrode to form the total chlorine working electrode.

The potassium halide salt added to the reagent composition may bepotassium bromide, and potassium chloride. Generally, the potassium saltis added in an amount such that the potassium salt is present in aconcentration of about of 0.05 to 2M typically about 0.25 to about 0.75M. One specific example is a 0.5M concentration of potassium bromide.

Suitable buffers include phthalate buffers, phosphate buffers. Phosphatebuffers include, for example disodium hydrogen phosphate, sodiumdi-hydrogen phosphate and mixtures thereof. Suitable phthalate buffersinclude potassium hydrogen phthalate. The buffer component is generallypresent in the reagent composition in the range of about 0.01 to about0.3 M. The pH of the buffer solution should be adjusted to the rangearound 3-4 pH is generally adjusted using a diluted hydrochloric acid(HCl), such as 0.1 M HCl.

In addition, the reagent composition will also have a polymericcomponent added to assist disposition of the potassium salt and bufferto the surface of the electrode. In addition, the polymeric material inthe reagent composition is used to retain reagent and buffer mixture onthe electrode surface, and stabilizing the response of electrochemicaldetection. Possible polymers include, for example, polyvinyl alcohol,sodium alginate, or other similar polyelectrolyte polymers. Generally,sodium alginate is used is used for the total chlorine sensor.Typically, the polymer is added in an amount of about 0.1 to about 2.0%by weight, based on the weight of the solution.

Total chlorine is measured amperometically by applying a voltage to theelectrode and measuring the current from the working electrode. Combinedchlorine is then determined by difference between the total chlorine andfree chlorine contents. Potassium bromide can react with free chlorineand combined chlorine as follows:

OCl⁻+2Br⁻+2H⁺↔Br₂+Cl⁻+H₂O

Cl₂+2Br⁻↔Br₂+2Cl⁻

NH₂Cl+2Br⁻+2H⁺↔Br₂+Cl⁻+NH₄+

RNHCl+2Br⁻+2H⁺↔Br₂+Cl⁻+RNH₃ ⁺

The liberated bromine is reduced electrochemically at the electrode asshown below:

Br₂+2e ⁻↔2Br⁻

Calcium Hardness Detection Reagent Composition

The calcium hardness sensor according to the invention measures thecontent of calcium ion in water by the amperometric analysis. Thereagent used in the calcium hardness reagent composition is anelectrochemical indicator for the detection of calcium ion and othercomplexometric indicators. The reagent composition for the hardnesselectrochemical sensor will generally contain an electrochemicalindicator for the detection of calcium ion and other complexometricindicators, a buffer component and a polymeric material. Typically,deionized water is used as the solvent for the composition and thecomponents are added so that the resulting composition has the componentpresent in an amount disclosed below.

The electrochemical indicator for the detection of calcium ion and othercomplexometric indicators are generally present in the reagentcomposition in an amount in the range of about 1 to 10 mM, typicallyabout 2-4 mM. Suitable compounds for this component include AlizarinRed, Alizarin Yellow CG, Alizarin Green, Alizarin Blue Black B, andEriochrome Black T. Of these, Alizarin Red S(3,4-dihydroxy-9,10-dioxo-2-anthracenesulfonic acid sodium salt) istypically used as an electrochemical indicator for the detection ofcalcium ion.

Suitable buffers include phthalate buffers, phosphate buffers and anacetate buffer. Phosphate buffers include, for example disodium hydrogenphosphate, sodium di-hydrogen phosphate and mixtures thereof. Suitablephthalate buffers include potassium hydrogen phthalate. The buffercomponent is generally present in the reagent composition in the rangeof about 0.01 to about 0.3 M. The pH of the buffer solution should beadjusted to the range around 3-4 pH is generally adjusted using adiluted hydrochloric acid (HCl), such as 0.1 M HCl.

In addition, the reagent composition will also have a polymericcomponent added to assist disposition of the Alizarin Red S, and bufferto the surface of the electrode. In addition, the polymeric material inthe reagent composition is used to retain reagent and buffer mixture onthe electrode surface, and stabilizing the response of electrochemicaldetection. Possible polymers include, for example, polyvinyl alcohol,polyvinylpyrrolidone, sodium alginate, or other similar polyelectrolytepolymers. Generally, sodium alginate or polyvinyl alcohol are used isused for the calcium hardness sensor. Typically, the polymer is added inan amount of about 0.05 to about 5.0% by weight, based on the weight ofthe solution. More preferably, the polymer is added in an amount ofabout 1.5 to 3% by weight, based on the weight of the solution.

Suitable buffers include phthalate buffer, phosphate buffer, and acetatebuffer in a pH range of 3.0 to 4.0. Suitable polymer materials mayinclude, but not limited to sodium alginate, polyvinyl alcohol,polyvinylpyrrolidone or other polyelectrolytes.

In another embodiment, the calcium hardness reagent is a copper (II)salt pre-mixed with a cationic ion exchange resin in lieu of a bufferand alizarine Red S. The copper/resin mixture is combined with apolymeric material, as described above, to prepare the reagentcomposition.

In another embodiment, the measurement of calcium ions in water is madeby the electrochemical detection of copper (II) ion that is releasedfrom cation exchange resin via ion exchange reaction. Copper salts inanhydrous or hydrated form are used as the source of copper (II) ions.Possible copper (II) salts include, but are not limited to, coppersulfate, copper chloride and copper nitrate. Copper (II)-bound cationexchange resin is prepared by soaking the resin in appropriate coppersalt solution, drying the treated resin, and milling into fine powder.The powered exchange resin is then mixed with a polymeric binder, asdescribed above, to prepare the reagent composition.

Suitable cation exchange resins include cation exchange resins commonlymade of styrene and cross-linking agent divinyl benzene, which arepost-functionalized to contain sulfonic acid groups, carboxylic acidgroups, or their corresponding salts. Suitable cation exchange resinsused to prepare the calcium hardness sensor include cation exchangeresins sold under the trade names Amberlite®, Amberlist®, Dowex®,Duolite® that bear sulfonic acid or carboxylic acid groups, or theircorresponding Na⁺ or H⁺ salt form.

Total Alkalinity Detection Reagent Composition

The total alkalinity sensor according to the invention measures thecontents of carbonate and bicarbonate in water by the amperometricanalysis using manganese compound as the reagent. Suitable manganesecompounds include, for example, manganese (II) salts, including but notlimited to manganese perchlorate, manganese acetate, manganese chloride,manganese nitrate, manganese sulfate. Typically, the reagent compositionmanganese (II) perchlorate as the reagent and a polymeric material. Themanganese (II) perchlorate reagent is generally present in aconcentration of 5 to 100 mM, typically between about 20 to 40 mM.

In addition, the reagent composition will also have a polymericcomponent added to assist disposition of the manganese (II) perchlorateto the surface of the electrode. In addition, the polymeric material inthe reagent composition is used to retain reagent on the electrodesurface, and stabilize the response of electrochemical detection.Possible polymers include, for example, polyvinyl alcohol,polyvinylpyrrolidone, sodium alginate, or other similar polyelectrolytepolymers. Generally, polyvinylpyrrolidone is used for the totalalkalinity sensor. Generally, the polymer is added in an amount of about0.5 to about 5.0% by weight, based on the volume of the solution.Typically the polymeric component will be about 1.5 to about 3% byweight of the composition.

Mn²⁺ ions complex with bicarbonate ions at a desirable pH range of7.2-7.6 in pool water as shown below:

Mn²⁺(aq)+2HCO₃ ⁻↔[Mn(HCO₃)₂]

The Mn-bicarbonate complex is then oxidized electrochemically at theelectrode as shown below:

[Mn(HCO₃)₂]↔Mn³⁺+2HCO₃ ⁻ +e ⁻

Cyanuric Acid Detection Reagent Composition

The cyanuric acid sensor according to the invention measures the contentof cyanuric acid in water by the amperometric analysis using transitionmetal (II) salts as the reagent. Suitable transition metals saltsinclude, for example, sulfates, nitrates, and chlorides. Typically, thereagent composition contains copper sulfate as the reagent and apolymeric material. The copper sulfate reagent is generally present in aconcentration of 5 to 100 ppm (as Cu), typically between about 5 to 20ppm.

The reagent composition has a polymeric component added to assistbinding of the transition metal salt (e.g., copper sulfate) to thesurface of the working electrode. In addition, the polymeric material inthe reagent composition is used to stabilize the response ofelectrochemical detection. Possible polymers include, for example,polyethylene glycol, polyvinyl alcohol, polyvinylpyrrolidone, or othersimilar polyelectrolyte polymers. Generally, polyvinyl alcohol is usedto prepare the cyanuric acid sensor. Generally, the polymer is added inan amount of about 0.05 to about 5.0% by weight, based on the volume ofthe solution. Typically the polymeric component will be about 0.05 toabout 1% by weight of the composition.

Copper Ion Detection Reagent Composition

The copper ion sensor according to the invention measures the coppercontent in water by squarewave voltammetry using a buffer deposited onthe working electrode. Typically, the buffer has pH ranging from 3 to 4,such as 3.5. Suitable buffers, for example, include phthalate,phosphate, citrate and acetate buffers with phthalate buffers beingpreferred.

Although not wishing to be bound by theory, it is believed that thepolymeric electrolyte's in each of the reagent compositions functions toreduce the current passed by the working electrode and stabilize thesignals to achieve sensitivity and consistency through creatingplurality of working electrodes, via the creation of individualcrystalline regions resulted from drying of reagents on top of theworking electrode. Crystals formed in the polymer matrix by drying inthe oven for specific amount of time and temperature. The polymer willact as a holding matrix for the crystals to be entrapped creatingapertures of crystals on the surface of the electrode. Therefore, eachcrystal will act as a working electrode via a controlled dissolution ofcrystals and polymeric surface. The number and sizes of these aperturesmay be controlled by reagent concentration and drying time andtemperature.

Other features may be present on the electrochemical sensor of thepresent invention. For example, an optional hood or cover may be placedover the electrodes to help protect the electrodes prior to use and toassist in holding the sample of water to be tested near the electrodes.

The shape of electrochemical sensors is generally rectangular in shape,as shown in FIGS. 1-5, but any other conventional shapes such as squareor circular type shapes may also be used without departing from thescope of the present invention.

Examples

A. Preparation of Free Chlorine Sensor

Preparation of Free Chlorine Detection Reagent Solution

A pH 7.4 buffer solution was prepared by dissolving 0.013 M of disodiumhydrogen phosphate, 0.007 M sodium di-hydrogen phosphate, and 0.45 Msodium chloride in deionized water. Then 1.33 wt. % polyethylene glycol(PEG) was added and dissolved in the solution. The solution was allowedto rest for 5 minutes and then 0.05 M N,N-diethyl-p-phenylenediaminesulfate salt (DPD) was added to the solution. The resulting mixture wasshaken vigorously to dissolve the DPD into the solution.

Deposition Procedure

A portion of the solution was deposited on a carbon working electrodepresent on an electrochemical sensor having a reference electrode and acounter electrode. The total amount of the solution deposited on theworking electrode was about 7.14 μL. Once deposition procedure wascompleted, the electrochemical sensor was carefully placed in an oven at100° C. for 15 minutes. The sensor was removed from the oven and allowedto cool for a period of time of at least 5 minutes.

B. Preparation of Total Chlorine Sensor

Preparation of Total Chlorine Detection Reagent Solution

A 0.1 M of potassium hydrogen phthalate pH 3.5 buffer solution wasprepared in deionized water. To this solution was added 18% (v:v) of 0.1M HCl. Then 0.03 g of sodium alginate per 15 mL of the buffer solutionwas dissolved in the solution. The solution was allowed to rest for 5minutes at room temperature. Next, 0.5 M potassium bromide was added tothe solution and the solution was vigorously shaken to dissolve thepotassium bromide in the buffer solution.

The final deposition solution concentrations of the solution was:potassium hydrogen phthalate about 0.1 M, hydrochloric acid about 0.0176M, potassium bromide about 0.5 M and sodium alginate about 0.2% (w:v).

Deposition Procedure

A portion of the total chlorine detection reagent solution was depositedon a carbon working electrode present on an electrochemical sensorhaving a reference electrode and a counter electrode. The total amountof the solution deposited on the working electrode was about 7.14 μL.Once deposition procedure was completed, the electrochemical sensor wascarefully placed in an oven at 100° C. for 15 minutes. The sensor wasremoved from the oven and allowed to cool for a period of time of atleast 5 minutes.

C. Preparation of Calcium Hardness Sensor

Preparation of Calcium Hardness Detection Reagent Solution

A 0.1 M of potassium hydrogen phthalate buffer solution (pH 3.4) wasprepared in deionized water. To this solution was added 18% (v:v) of 0.1M HCl. Then 0.03 g of sodium alginate per 15 mL of the buffer solutionswas dissolved into the solution. Then 0.03 g of sodium alginate wasdissolved in the solution per 15 mL of the solution. The solution wasallowed to rest for 5 minutes at room temperature. Next 0.003 M AlizarinRed S (3,4-dihydroxy-9,10-dioxo-2-anthracenesulfonic acid sodium salt)was added to the solution and to the solution was vigorously shaken todissolve the Alizarin Red S into the buffer solution.

The final deposition solution concentrations of the solution was:potassium hydrogen phthalate about 0.1 M, hydrochloric acid about 0.0176M, Alizarin Red S about 3 mM, and sodium alginate about 0.2% (w:v).

Deposition Procedure

A portion of the calcium hardness reagent solution was deposited on acarbon working electrode present on an electrochemical sensor having areference electrode and a counter electrode. The total amount of thesolution deposited on the working electrode was about 7.14 μL. Once thedeposition procedure has been completed, the electrochemical sensor wascarefully placed in an oven at 50° C. for 20 minutes. The sensor wasremoved from the oven and allowed to cool for a period of time of atleast 5 minutes.

D. Preparation of Total Alkalinity Sensor

Preparation of Total Alkalinity Detection Reagent Solution

The total alkalinity reagent composition was prepared by dissolving 2%by weight of polyvinylpyrrolidone (0.3 g/15 mL) in deionized water toprepare a solution. To this solution, 40 mM (152 mg/15 mL) ofMn(ClO₄)₂.6H₂O was added. The mixture was shaken until the componentswere dissolved. The resulting solution was the total alkalinity reagentsolution.

Deposition Procedure

A portion of the total alkalinity reagent solution was deposited on acarbon working electrode present on an electrochemical sensor having areference electrode and a counter electrode. The total amount of thesolution deposited on the working electrode was about 7.14 μL. Oncedeposition procedure was completed, the electrochemical sensor wascarefully placed in an oven at 100° C. for 15 minutes. The sensor wasremoved from the oven and allowed to cool for a period of time of atleast 5 minutes.

E. Preparation and Testing of Alternate Calcium Hardness Sensor

Preparation of Calcium Hardness Detection Reagent Suspension

The calcium hardness reagent composition was prepared by dissolving 2%(w/w) polyvinyl alcohol (PVA) in deionized water to prepare a PVAsolution. To the PVA solution, a powdered Cu (II)-bound exchange resinwas added. The exchange resin used was an Amberlite® IR-120 H⁺ cationexchange resin (commercially available from the Dow Chemical Company).The bound resin was prepared by soaking 2 grams of resin beads in 250 mLof 0.02 M of Cu(SO₄)₂ solution for 48 hours. The process was repeatedonce more and then the resin beads were washed with deionized water,dried and milled into a fine powder. The fine powder was added to thePVA solution to form the calcium hardness reagent suspension.

Deposition Procedure

A portion of the calcium hardness reagent suspension was deposited on acarbon working electrode present on an electrochemical sensor having areference electrode and a counter electrode. The total amount of thesuspension deposited on the working electrode was about 7.14 μL. Oncedeposition procedure was completed, the electrochemical sensor wascarefully placed in an oven at 100° C. for 15 minutes. The sensor wasremoved from the oven and allowed to cool for a period of time of atleast 5 minutes.

Testing

The calcium hardness sensor was evaluated using amperometric analysisagainst five (5) stock solutions with increasing levels of calcium ionsto approximate increasing levels of calcium hardness in a pool of water:0 ppm, 50 ppm, 100 ppm, 200 ppm and 400 ppm. The results are shown inFIG. 6.

F. Preparation and Testing of Cyanuric Acid (CYA) Sensor

Preparation of CYA Detection Reagent Solution

The CYA detection reagent composition was prepared by dissolving 0.1% byweight of polyvinyl alcohol (15 mg/15 mL) in deionized water to preparea solution. To this solution, 10 ppm as Cu was added. The mixture wasshaken until the components were dissolved. The resulting solutionformed the CYA detection reagent solution.

Deposition Procedure

A portion of the CYA detection reagent solution was deposited on acarbon working electrode present on an electrochemical sensor having areference electrode and a counter electrode. The total amount of thesolution deposited on the working electrode was about 7.14 μL. Oncedeposition procedure was completed, the electrochemical sensor wascarefully placed in an oven at 100° C. for 10 minutes. The sensor wasremoved from the oven and allowed to cool for a period of time of atleast 5 minutes.

Testing

The CYA detection sensor was evaluated using amperometric analysisagainst three (3) stock solutions with a pH of 7.6 and increasing levelsof CYA to approximate increasing levels of CYA in a pool of water: 0ppm, 50 ppm, and 100 ppm. The results are shown in FIG. 7.

G. Preparation and Testing of Copper Ion Sensor

Preparation of Copper Ion Detection Reagent Solution

The copper electrode modifying reagent composition was prepared bydissolving 0.1 M of potassium hydrogen phthalate (0.306 g) in 15 mL ofdeionized water. To this solution, 18% (v:v) of 0.1 M HCL was added toadjust the pH to about 3.5. The resulting solution formed the copperdetection reagent solution.

Deposition Procedure

A portion of the copper detection reagent solution was deposited on acarbon working electrode present on an electrochemical sensor having areference electrode and a counter electrode. The total amount of thesolution deposited on the working electrode was about 7.14 μL. Oncedeposition procedure was completed, the electrochemical sensor wascarefully placed in an oven at 100° C. for 10 minutes. The sensor wasremoved from the oven and allowed to cool for a period of time of atleast 5 minutes.

Testing

The copper ion detection sensor was evaluated using square wavevoltammetry against four (4) stock solutions with increasing levels ofcopper to approximate increasing levels of copper in a pool of water: 0ppm, 0.2 ppm, 1 ppm, and 2 ppm. The results are shown in FIG. 8.

While the invention has been described above with references to specificembodiments thereof, it is apparent that many changes, modifications andvariations can be made without departing from the invention conceptdisclosed herein. Accordingly, it is intended to embrace all suchchanges, modifications, and variations that fall within the spirit andbroad scope of the appended claims.

What is claimed is:
 1. A electrochemical sensor for the detection andanalysis of an analyte in a solution, the electrochemical sensorcomprising: (i) an electrically non-conductive support; (ii) a pluralityof electrodes on the support, each electrode comprising an electrodematerial and having a first surface and an opposite second surface, thefirst surface facing towards the support and the second surface facingaway from the support, the plurality of electrodes comprising a. areference electrode, b. a counter electrode, and c. a working electrode;and (iii) a reagent composition containing a reagent for detecting ananalyte applied directly to the second surface of the working electrode,such that the reagent composition essentially completely covers thesecond surface of the working electrode or dispersed throughout theelectrode material of the working electrode; wherein the reagentcomprises an indicator for the analyte.
 2. The electrochemical sensoraccording to claim 1, comprising one to eight working electrodes.
 3. Theelectrochemical sensor according to claim 1, wherein the reagentcomposition completely covers the entire second surface of the workingelectrode.
 4. The electrochemical sensor according to claim 1, whereinthe indicator is for copper.
 5. The electrochemical sensor according toclaim 4, wherein the indicator for copper comprises a buffer.
 6. Theelectrochemical sensor according to claim 5, wherein buffer comprises aphthalate buffer, a phosphate buffer, a citrate buffer, or an acetatebuffer.
 7. The electrochemical sensor according to claim 1, wherein thereagent composition applied to, or dispersed throughout, the workingelectrode comprises a reagent for analyzing water hardness.
 8. Theelectrochemical sensor according to claim 7, wherein the reagentcomposition comprises an indicator for calcium, a cation exchange resin,and a polyelectrolyte polymer.
 9. The electrochemical sensor accordingto claim 8, wherein the indicator for calcium is a copper salt.
 10. Theelectrochemical sensor according to claim 9, wherein the copper salt isselected from the group consisting of copper sulfate, copper chlorideand copper nitrate.
 11. The electrochemical sensor according to claim 9,wherein the copper salt is copper sulfate.
 12. The electrochemicalsensor according to claim 11, wherein the copper sulfate is coppersulfate heptahydrate.
 13. The electrochemical sensor according to claim1, wherein the reagent comprises a transition metal salt is selectedfrom the group consisting of transition metal sulfates, transition metalnitrates and transition metal chlorides.
 14. The electrochemical sensoraccording to claim 13, wherein the reagent composition further comprisesa polyelectrolyte polymer.
 15. The electrochemical sensor according toclaim 14, wherein the polyelectrolyte polymer comprises sodium alginate,polyethylene glycol, polyvinyl alcohol, or polyvinylpyrrolidone.
 16. Theelectrochemical sensor according to claim 13, wherein the transitionmetal of the transition metal salt is copper.
 17. The electrochemicalsensor according to claim 1, further comprising a plurality ofelectrical contacts, wherein each of the electrodes is electricallyconnected with a separate contact.
 18. The electrochemical sensoraccording to claim 1, wherein the reference electrode comprises asilver/silver chloride electrode, the counter electrode comprises acarbon electrode and the working electrode comprises a carbon electrode.19. The electrochemical sensor according to claim 1, wherein there are aplurality of working electrodes, wherein the working electrodes eachhave a reagent composition applied to the second surface of each workingelectrode, or dispersed throughout the electrode material of eachworking electrode, the reagent composition is selected from the groupconsisting of a composition containing a reagent for detecting freechlorine, a composition containing a reagent for detecting totalchlorine, a reagent composition for detecting water hardness, a reagentcomposition for detecting total alkalinity, a reagent composition fordetecting cyanuric acid, and a reagent composition for detecting copper.20. A method of analyzing water, the method comprising: providing asample of water containing an analyte to be measured; providing, in adisplay device, an electrochemical sensor including, (i) an electricallynon-conductive support; (ii) a plurality of electrodes on the support,each electrode comprising an electrode material and having a firstsurface and an opposite second surface, the first surface facing towardsthe support and the second surface facing away from the support, theplurality of electrodes including a. a reference electrode, b. a counterelectrode, and c. a working electrode; and (iii) a reagent compositioncontaining a reagent for detecting an analyte applied directly to thesecond surface of the working electrode, or dispersed throughout theelectrode material of the working electrode; and contacting the sampleof water with the sensor to measure the analyte.
 21. The methodaccording to claim 20, wherein there are a plurality of workingelectrodes, wherein the working electrodes each have a reagentcomposition applied to the second surface of each working electrode, ordispersed throughout the electrode material of each working electrode,the reagent composition is selected from the group consisting of acomposition containing a reagent for detecting free chlorine, acomposition containing a reagent for detecting total chlorine, a reagentcomposition for detecting water hardness, a reagent composition fordetecting total alkalinity, a reagent composition for detecting cyanuricacid, and a reagent composition for detecting copper.